The use of towing warps in trawling and marine seismology is well known. In trawling the towing warp is generally referred to as a “warp” or “tow warp”. In marine seismology the towing warp is generally referred to as a “superwide cable” (also known as “wide tow ropes”, “superwides” and “main tow ropes”), the term “rope” and the term “cable” to be interchangeable for purposes of the present disclosure.
In trawl fishing, a trawler deploys a tow warp to tow upon a trawl system including a trawl net and often paravanes known as “trawl doors”. A main problem in trawl fishing is that a heavy weight of steel wire cable for use as tow warps makes trawling vessels unstable and dangerous, having been responsible for many capsizes and losses of life. Other problems with steel wire include premature failure from oxidation and electrolytic degradation. In order to resolve these problems associated with steel wire tow warps, many trawling vessels are using towing warps formed of synthetic fibers. However, a main problem with such synthetic fiber formed towing warps is that they tend to prematurely break both in the area proximal (including “at”) a sheave (including “block”) upon which the towing warps bend and rest, as well as proximal the connection point to a paravane. The same problem exists with the deployment of synthetic towing warps in marine seismology.
Furthermore, in marine seismology at sea, a seismic ship deploys a streamer or cable behind the ship as the ship moves forward. Multiple receivers are typically towed behind the ship on streamers in an array. Streamers typically include a plurality of receivers. A seismic source is also towed behind the ship, with both the source and receivers typically deployed below the surface of the ocean. Streamers typically include electrical or fiber-optic cabling for interconnecting receivers and seismic equipment on the ship.
Streamers are usually constructed in sections 25 to 100 meters in length and include groups of up to thirty-five or more ideally uniformly spaced receivers. The streamers may be several miles long, and often a seismic ship trails multiple streamers, with ideally a uniform lateral separation between the streamers, to increase the amount of seismic data collected. Operating at a typical production speed of 4 to 5 knots and towing in excess of 50 tons of instrument-laden equipment in the water, a great deal of drag induced tension is generated. Similarly, the number and length of streamers to be deployed, as well as the lateral separation to be maintained between streamers, dictates the size of diverters, or paravanes, that must be deployed with the array, and also has a major impact on the tension that ultimately is transferred to a seismic ship through the superwides.
The amount of equipment towed behind a ship is generally dictated by the requirements of the job. The equipment and cables being towed create a drag on the ship. The more equipment and cables that are towed behind a ship, the more drag is created, thus the more lateral spreading force is required to achieve desired separations between cables, and the more tension is transferred to the seismic ship through the superwides. This results undesirably in high stresses in the superwides, that ultimately lead to premature failure of the superwides at a region of the connection of the superwides to the diverters. The premature failure of the superwide cables in this one region results in substantial technical complications and financial losses as either the superwide cables must be premature replaced, i.e. before the normal safe working life span of the majority of the superwide cable is reached, or breakage occurs resulting in large equipment failures and operational losses.
Attempts at strengthening a rope or cable in the vicinity of its connection to an object, such as disclosed in U.S. Pat. No. 4,184,784, have failed to solve the problem and have not been accepted by the industry. These attempts mainly include incorporation into and between strands of an already formed rope of other strands formed of a plurality of fibers. The incorporation of the other strands is accomplished by opening up the braid structure of a rope and inserting into and between the strands forming the already formed rope the other strands so as to accomplish a tapered transition from the undisturbed portion of the already formed rope to the portion into which the other strands are being incorporated and generate a strengthened and enlarged portion to the rope. In such known teachings, the strands being incorporated into the rope are either braided or twisted strands where the strands include at least one hundred fibers and there is no knotting, due to the fact that knotting of the Inserted other strands to those strands already present in the already formed portion of the rope is known to cause rapid destruction of the rope, thus the use of knotting in such applications being contrary to the trend of the industry, against the state of the art and against the belief of those in the industry. As mentioned supra, such constructions and methods for ropes with an increased diameter and breaking strength in a certain region have failed to be accepted into the industry.
Furthermore, attempts at altering the material composition of the rope by this method, especially by splicing into a rope formed of a super fiber material such as UHMWPE (e.g. “Dyneema®”) another rope formed of an elastic material such as Polyamide (e.g. “Nylon”), have proved to be unreliable, with failure of the rope at the splice junction being the norm, and have thus been rejected by the industry.
Thus, it is readily apparent that both the tapering of ropes used for towing warps as well as the alteration of ropes used for towing warps from one material to another material is contrary to the trend in the industry and against the state of the art in the industry.
Both in trawl fishing as well as in marine seismology an accepted principle is that steel wire is more tolerant of bending fatigue than are synthetic cables formed of UHMWPE due to the fact that the steel wire is more elastic than is the cable formed of UHMWPE, it being accepted in the industry that a more elastic cable is more able to tolerate bending forces leading to bending fatigue induced failure than is a less elastic cable. Similarly, it is accepted in the industry that a more elastic material is better able to tolerate bending forces leading to bending fatigue induced failure than is a less elastic material, and that therefore a cable such as a tow warp formed of a more elastic construction is better able to tolerate bending and is more resistant to bending fatigue induced failure than is a tow warp formed of a less elastic material.
Thus, due for one to the greater failure rate of synthetic tow warps vs. steel wire tow warps in the area proximal a sheave and/or other block from which depends a tow warp, despite the much increased dangers of recoil induced fatality and crippling of workers, vessel capsize as well as economic disadvantages associated with reduced hold capacity resultant of displacement needs caused by steel wire tow warps, many trawl fishing entities as well as entities conducing marine seismology continue to use steel wire tow warps rather than synthetic tow warps, including synthetic tow warps formed of super fibers such as fibers formed of UHMWPE.
Thus, it can readily be appreciated that a long felt need exists in the industry for a tow warp construction that retains its useful dimensions for a greater period of time than known tow warp constructions in and about the region of its location to a sheave and/or other block that is used in deployment of the tow warp.
Thus, also it can readily be appreciated that a long felt need exists in the industry for a tow warp construction where such tow warp construction retains its useful dimensions in and about the region of its location to a paravane for a greater period of time than known tow warp constructions and where such tow warp construction is lighter in weight than steel both in air as well as in water and preferably is made of a material that is less elastic and has less ability to store kinetic energy and thus to recoil than does steel wire.
Thus also, it can readily be appreciated that a long felt need exists in the industry for a tow warp construction that retains its useful dimensions for a period of time that is similar to and preferably at least as great as the expected safe working life span of that portion of a tow warp that is not normally experiencing premature failure as a result of its proximity to a paravane.
Thus also, it can readily be appreciated that a long felt need exists in the industry for a tow warp construction where such tow warp construction retains its useful dimensions in and about the region of its location to a paravane for a greater period of time than known tow warp constructions where such period of time is sufficient to permit full use of the expected safe working life span of the majority of the tow warp construction without unduly risking premature failure of the tow warp in the region of its connection to a paravane and without unduly risking resultant substantial technical complications and financial losses as a result of such premature failure.
Thus also it can readily be appreciated that a long felt need exists in the industry for a tow warp construction having any of: at least one strength member; an optical conductor; an electrical conductor; a sensor; and any other instrument where such tow warp construction retains its useful dimensions longer than known tow warp constructions thereby permitting less frequent replacement of the tow warp, and ideally permitting full use of the cables full life expectancy.
In addition to trawlers and seismic ships, other marine vessels, such as oceanographic ships and commercial tug boats and pilot boats also may tow cabling or equipment for which a longer lived tow warp would be beneficial. Furthermore, a synthetic rope constructed according to the present disclosure is useful also for deep water oil rig mooring lines and other deep water mooring lines.